Human immunodeficiency virus (HIV) infection is driving the re-emergence of opportunistic tuberculosis (TB) as a global health emergency, and is strongly associated with the development of multi- or extensively- drug resistant TB (MDR-, XDR-TB). Currently there are no animal models to study HIV/Mtb co-infection due to the human host tropism of HIV. The BLT humanized mouse model is being rapidly applied to study several pathogens where suitable animal models are deficient, including HIV, malaria, and HIV/HCV co-infection. The objective of this proposal is to develop a small animal model of HIV/Mtb co-infection in the humanized mouse for immunological studies critical to Mtb vaccine development. The central hypothesis is that HIV infection will increase the pathogenesis of Mtb and compromise vaccine-induced cell-mediated immunity to Mtb in a humanized mouse model of HIV/Mtb co-infection. The rationale for the proposed research is that a small animal model of human HIV/Mtb co-infection would greatly enhance progress towards understanding these and other mechanisms whereby HIV suppresses CMI to Mtb and accelerate design and screening of TB vaccines for HIV+ populations. The specific aims to test this central hypothesis are 1) To develop a relevant mouse model to study the pathogenesis of Mtb and HIV/Mtb infection and 2) To determine how HIV alters protective CMI to Mtb in M. bovis BCG-vaccinated, humanized mice. These aims will be accomplished by using the NOD-SCID/3cnull mouse engrafted with human fetal liver and thymic tissue, and injected intravenously with CD34+ fetal liver cells from the same tissue source. Differences in Mtb disease severity due to HIV infection will be monitored by in vivo fluorescent quantification (tdTomato Mtb H37Rv), pathology and bacterial load in tissues, and survival. Alterations in CMI in naive and BCG (heat-inactivated)-vaccinated animals due to HIV will be determined by analysis of: cytokine profiles;leukocyte distribution and organization, and T cell effector molecule expression, at sites of Mtb infection;and ex vivo antimycobacterial activity of CD4+ and CD8+ T cells against Mtb-infected macrophages. The proposed work will establish a small animal model of HIV/Mtb co-infection with a defined magnitude, time course, and outcome of disease due to Mtb. Further, specific mechanisms of post-vaccination antimycobacterial T cell function that are impaired by HIV will be identified and assessed relative to protection from Mtb challenge. This co-infection model will be a powerful research tool for discoveries in the basic biology of co-infection and disease intervention. Development of this model is significant, as these results will provide new opportunities to identify the mechanisms whereby HIV compromises the protective CMI response to Mtb. The positive impact of this model system will be greatly enhanced capabilities to design and screen innovative prophylactics and therapeutics for TB to use in populations with HIV-compromised immune systems. PUBLIC HEALTH RELEVANCE: The proposed research is relevant to public health because it will significantly advance our fundamental understanding of how HIV dysregulation of the immune system promotes the susceptibility to Mycobacterium tuberculosis. The results of these studies will enable informed guidance for the development of vaccines and therapeutics to protect HIV+ patients from tuberculosis.